Audio circuitry may be implemented (at least partly on ICs) within a host device, which may be considered an electrical or electronic device and may be a mobile device. Examples devices include a portable and/or battery powered host device such as a mobile telephone, an audio player, a video player, a PDA, a mobile computing platform such as a laptop computer or tablet and/or a games device.
Battery life in host devices is often a key design constraint. Accordingly, host devices are capable of being placed in a lower-power state or “sleep mode.” In this low-power state, generally only minimal circuitry is active, such minimal circuitry including components necessary to sense a stimulus for activating higher-power modes of operation. In some cases, one of the components remaining active is a capacitive microphone, in order to sense for voice activation commands for activating a higher-power state. Such microphones (along with supporting amplifier circuitry and bias electronics) may however consume significant amounts of power, thus reducing e.g. battery life of host devices.
It is known to use a speaker (e.g. a loudspeaker) as a microphone, which may enable a reduction in the number of components provided in a host device or the number of them kept active in the low-power state. Reference in this respect may be made to U.S. Pat. No. 9,008,344, which relates to systems for using a speaker as a microphone in a mobile device. However, such systems are considered to be open to improvement when both power performance and audio performance are taken into account.
It is desirable to provide improved audio circuitry, in which both power performance and audio performance reach acceptable levels. It is desirable to provide improved audio circuitry to enable a speaker (e.g. a loudspeaker) to be used both as a speaker and a microphone (e.g. simultaneously), with improved performance.